In recent years, automobiles are equipped with various electronic devices for performing various electronic controls. These electronic devices are connected to one another through a network. CAN (controller area network) has become widespread as one of the network protocols established in an automobile.
In a network configured by CAN, a plurality of ECUs (electronic control unit) perform communication through a HUB node. The HUB node may operate as a relay node. Further, in the CAN system, a data frame transmitted from one ECU is received by all other ECUs. In other words, the CAN system provides broadcast communication. According to an ID added to a received data frame, each ECU obtains a necessary data frame and discards an unnecessary data frame.
In the CAN network having the above-described configuration, a function that detects an abnormal frame may be requested. In this case, the CAN network has a communication monitoring device. The communication monitoring device may be implemented by a gateway device. The gateway device may connect CAN to other networks (for example, the Internet). In the following description, it is assumed that the gateway device has a function that detects an abnormal frame.
As described above, the CAN system provides broadcast communication. Thus, the gateway device can receive all frames that are broadcasted in the network. Then, the gateway device detects an abnormal frame by analyzing each of the received frames. Preferably, the gateway device can identify a source node of the detected abnormal frame.
As a related technology, a transmission source tracking system that tracks a transmission source of a packet in a network including a plurality of relay devices has been proposed (for example, Japanese Laid-open Patent Publication No. 2006-148594).
According to CAN, a method for identifying an ECU that is a source node of an abnormal frame is not definitively determined. Further, information that identifies a source node (for example, a source address) is not added to a frame that is transmitted in the CAN system. Thus, it is difficult for a gateway device to identify an ECU that is a source node of an abnormal frame when the abnormal frame is detected.
Even in a network in which information that identifies a source node is not added to a transmitted frame, the gateway device may be able to identify a source node of an abnormal frame if each relay node stores related information of all forwarded frames. However, in this configuration, each of the relay nodes has to be provided with a large-capacity memory.
Note that this problem occurs not only in the CAN system, but it may also occur in a network in which information that identifies a source node is not added to a transmitted frame.